LING330: Quiz #4 Flashcards
Two types of sounds
PERIODIC: pressure wave of a specific shape repeated multiple times (ex: musical notes)
APERIODIC: moment to moment pressure waves are more random; no repeating patterns (ex: radio static, sound of rustling leaves, etc)
Category of aperiodic sound
TRANSIENT: instantaneous (ex: breaking glass, snapping fingers, etc); momentary disturbance that isn’t drawn out or repeated
What is a waveform of a sound?
Graphical representation of sound pressure changes over time
X AXIS: time in seconds (usually milliseconds)
Positive vs negative values in waveforms
Positive: moments of higher pressures (compression)
Negative: moments of lower pressure (rarefaction)
0 value: equilibrium
Period vs frequency (acoustics)
Period: time required for each cycle
Frequency: number of cycles in a given amount of time
Most basic formula in acoustics
F=1/P
F=frequency
P=period
Amplitude
Displacement of the “pendulum” (how far it moves/the distance from A to B)
Depends on how much energy is put into the system
What happens when there is a gradual loss of energy and amplitude from cycle to cycle (acoustics)?
Damping!
LIGHTLY damped system= energy loss is GRADUAL and oscillations CONTINUE for a long time
HIGHLY damped system= energy loss is QUICK and oscillations DIE DOWN quickly
**speech vibrations=fast oscillations=loss of energy between cycles is negligible; takes thousands of cycles for energy to die out (fair to say we are dealing with UNDAMPED systems)
What does one full cycle include in acoustics?
Motion to the right (positive displacement)
Motion to the left (negative displacement)
Speech is what kind of wave?
Complex sine wave (graphs geometric sin function of an angle as it moves from 0 degrees to 360 degrees)
Cosine wave
Based on cosin function
Same shape as sine wave BUT begins at maximum value of 1 not 0
Phase shift
Difference in starting point of a wave
Sinusoid
Any wave that has the shape of a sine wave no matter what the differences in phase
Cosine wave graphs what?
Instantaneous velocity of the pendulum bob (how fast the bob is moving at a given time in a given direction)
Positive 1=PEAK velocity in a RIGHTWARD direction
Negative 1=PEAK velocity in a LEFTWARD direction
0 velocity=no movement at all
Three reasons that sinusoids are important for acoustic phonetics
1- any oscillating system whose PERIOD and VELOCITY have an inverse relationship and captured by cosine and sine waves is said to be in SIMPLE HARMONIC MOTION
2- mathematics of sinusoidal motion=well understood (we only need 3 numbers to describe it perfectly: frequency, amplitude and phase - but phase isn’t that important for speech analysis)
3- every kind of vibration can be described as the sum of a set of simple sinusoids of different frequencies and amplitudes
Simple harmonic motion
Period and velocity have inverse relationship
Captured by sine and cosine waves
Amplitude (displacement) moves regularly back and forth (from positive to negative)
Velocity=0 when displacement=greatest and vice versa
Ex: clock pendulums, playground swings, springs, etc
Important difference between motion of a tuning fork vs a pendulum
Oscillations of the tuning fork take place within the range of frequencies and amplitudes to which the human ear is sensitive
Harmonics
Differing frequencies and amplitudes of the component harmonics give the sound it’s quality (makes violin and piano sound different)
Formula that describes the relationship between period and wavelength
Distance = rate * time
Distance vs rate vs time
Talking about waves:
Distance = wavelength (distance from one peak to the next)
Rate = speed at which motion propagates from one particle to the next (depends on properties of medium that wave is moving through, ex: water vs syrup)
Time = period (amount of time it takes to generate one full cycle)
Transverse vs longitudinal waves
TRANSVERSE: motion of individual particles is PERPENDICULAR to the motion of the wave (moves sideways; ex: stadium wave, ripples on a pond, a whip)
LONGITUDINAL: motion of individual particles is PARALLEL to the motion of the wave (ex: sound waves)
Describe a special kind of longitudinal wave
PRESSURE WAVE
made up of COMPRESSION followed by RAREFACTION (coils of spring are stretched out) moving down a line
Pressure variations vs range in sound waves
Not very big variations, but ear is sensitive to large range of pressures (depends on intensity of wave)
Amount of energy present in the wave is called its…
Intensity
Both how big and how fast the pressure variations are (amplitude and frequency)
What scale is used to measure intensity range of sound waves
Logarithmic scale
Values based on exponents or values of 10
Specifically DECIBEL scale
Formula for decibel
Decibel (dB) = 10 times the log of the ratio of two sound intensities
Four types of acoustic signals
1- pure tones (sine waves)
2- complex signals/speech (periodic and quasi-periodic)
3- noise
4- impulse (transient)
Sound waves
Differences in air (usually) pressure
An energy source forces oscillation of molecules
Radiate out from a source due to an increase in pressure (which then increases the pressure at that location, forcing those molecules out into areas where air pressure is lower)
Low air pressure at the source causes air molecules to rush into that area, creating a chain reaction of low pressure to spread through the area
Are sound waves longitudinal or transverse?
Longitudinal
Oscillate perpendicular to the direction of the waves itself
(Transverse means that molecules move perpendicular to direction of wave)
What kind of wave is speech?
Complex sine wave
What are the properties of a sine wave? (3)
Frequency
Amplitude
Phase
4 properties of sound waves
1- rate of change in air pressure (frequency, pitch)
2- magnitude of changes (amplitude, intensity, loudness)
3- relative position of points within a wave or between waves (phase)
4- speed/length
Damping
Gradual loss of amplitude from cycle to cycle in oscillation
Oscillogram
Aka waveform
Visual representation of air pressure variations over time
Permits analysis and preservation of ephemeral speech signal
Amplitude
Distance of oscillation of molecules
Represented as:
Maximal displacement from zero line (average air pressure)
Greater amplitude=greater distance of oscillation
=greater distance between air pressure maxima and minima
=perception of “louder”
Phase
The interval between 2 maxima
A way of relating 2 signals (waves) to each other
Measured in degrees
